The inner structure of an electro-dynamic shaker is shown in FIG. 1. The field coil 4 is built in the magnetic circuit 2. The armature 6 is supported by the air suspension 8 so that it can move along the centre line of the shaker. Specimen of the vibration test can be attached at the head of the armature 6. The drive coil 10 is wound at the bottom of the armature 6.
When DC current is fed to the field coil 4, a static magnetic field is generated at the gap 12. The drive coil 10 is set in this gap 12, and AC current fed to the drive coil 10 yields a vibratory movement of the armature 6, and this motion is fed to the specimen attached on the armature 6 as the vibration for testing.
The air duct 14 is attached at the bottom of the magnetic circuit 2, and the other end of the duct 14 is connected to the blower 16. With rotating the blower 16, air-flow from the air-intake 18 at the top of the magnetic circuit 2 to inside is generated, and this air-flow cools the field coil 4 and the drive coil 10.
Although an air-cooled system is used for explanation here, this invention can be applied also to water-cooled systems by focusing attention to the power consumption or noise generation of the cooling apparatus.
A block diagram of a vibration test system using the electro-dynamic shaker in the FIG. 1 is shown in FIG. 2. Specimen 20 is attached on the top of the armature 6. Field current is fed to the field coil 4 by the field power supply 25. The blower power supply 27 feeds the power to the blower 16. Frequency spectrum of the desired vibration to be applied to the specimen is defined as the control reference spectrum for the vibration controller 22. The drive signal from the vibration controller 22 is amplified by the amplifier 24 and fed to the drive coil 10. Yielded vibration is measured by the acceleration sensor 30 attached on the armature 6, and this response signal is returned to the vibration controller 22. The spectral analysis of the response signal is carried out by the vibration controller 22, and the spectrum of the drive signal is modified so that the matching of the response spectrum to the reference spectrum will be improved in the next control loop. And the drive waveform signal is generated based on the new drive spectrum, and the drive signal is outputted to the amplifier 24. In such a way, generation of the desired vibration for the specimen to be tested is accomplished.
In addition to the above explained case of Random vibration test (random vibration having a required power spectral density is given to the specimen), Sine vibration test at a fixed frequency, Swept-sine vibration test that gives sinusoidal vibration of which frequency varies with time, and SOR (Sine-On-Random) or ROR (Random-On-Random) tests that are based on a combination of the former tests, Shock test that gives a pulse-shaped acceleration change described as a short time waveform, or Waveform replication test that regenerates the recorded vibration waveform for testing the specimen just as it was, are popularly conducted using the electro-dynamic shaker systems.
In the conventional electro-dynamic shaker systems, the value of the field coil current fed by the field power supply 26 is decided based on the maximum rating force of the corresponding system and fixed at the moment of the shipping at the manufacturer and could not be changed by the operator. So, it was impossible for the operator to carry out a test with reducing the field current value in case of only small excitation force is required to reduce the total power consumption. Even when it was allowed for the operator to change the field current by himself by some means, it was not easy to use appropriately, because professional knowledge and skill were required to predict the influence of the change of the field current setting correctly.
For instance, when the field current is reduced, then the drive current must be increased to keep the excitation force constant. So, reduction of the field current does not directly mean the reduction of total power consumption. A good balance between the field current and the drive current must be taken to achieve energy-saving.
In the Japanese laid-open patent application JP-A-200113033, there is disclosed a method to reduce the field current and its power consumption in the field coil when the required force is small. But when the increase of the drive power (caused by the drive current increase) as the result of the field current reduction is larger, then energy-saving of the total system cannot be achieved.
In addition, the Japanese laid-open patent application JP-A-200113033 discloses a method to reduce the blower rotation for the purpose of quiet operating when the required force is small. But just the same as above, it intends to solve the heat problem with focusing on the field current only. So, even if the purpose of quiet operating is looked as if it has been solved, the increase of heat generation by the drive current is not solved at all.
This invention provides apparatus that can calculate the optimal operating condition of the electro-dynamic shaker system in respect of the criteria such as energy-saving or quiet operating with regard to the performance limitations of the system and with solving the above mentioned problems.